NITROGENOUS SOIL CONSTITUENTS 



57 



occasioned by the hypoxanthine in tiicsc cultures containing Ki 

 parts per million of NH3 as nitrate is only 3 per cent, while the 

 8 parts per million nitrate series was 14 per cent and the no 

 nitrate series was 41 per cent. 



With still larger amounts of nitrate present the additional 

 effect was less certain. In some cases the hypoxanthine produced 

 an increase in growth, in others a slight decrease, so that the 

 result in the two sets of cultures with these higher nitrate con- 

 tents was practically alike. In other words, no additional effect 

 caused by the addition of the hypoxanthine is definitely shown 

 on the green weight, but an effect was produced, nevertheless, 

 in that less nitrate was consumed w^hile this equal growth took 

 place, as will be shown. 



Influence of hypoxanthine on absorption of fertilizer salts 



The foregoing discussion has shown clearly the influence of 

 hypoxanthine on growth and its effect in cultures containing no 

 nitrate. There remains to be discussed the effect of hypoxan- 

 thine on the removal of nutrients from the solution during the 

 growth of the plant. Mention has already been made of the fact 

 that the concentration differences produced by the growth of the 

 plants in the various cultures was determined by making an 

 analysis for nitrate at the termination of ever}^ three-day change, 

 and of the phosphate and potassium on a composite of the solu- 

 tions from the four changes. It is thus possible to compare the 

 results obtained under the so-called normal conditions and where 

 100 parts per million of hypoxanthine were present in the solu- 

 tion. 



The sum total of P2O5, NH3, and K2O removed from solution 

 by the growing plants in the cultures containing all three of 

 these constituents was 1429.1 mgms. under the normal conditions 

 and 1134.2 mgms. in the hypoxanthine set. The figures show 

 the total of plant nutrients removed to be less in the hypoxan- 

 thine set although the green weight in this set was greater than 

 in the normal set. WTien the removal of the individual fertilizer 

 elements, P2O5, NH3 and K2O, respectively, from the culture 



